Solve for $x$ and $y$ using substitution. ${-2x+y = -7}$ ${x = -2y-9}$
Answer: Since $x$ has already been solved for, substitute $-2y-9$ for $x$ in the first equation. ${-2}{(-2y-9)}{+ y = -7}$ Simplify and solve for $y$ $4y+18 + y = -7$ $5y+18 = -7$ $5y+18{-18} = -7{-18}$ $5y = -25$ $\dfrac{5y}{{5}} = \dfrac{-25}{{5}}$ ${y = -5}$ Now that you know ${y = -5}$ , plug it back into $\thinspace {x = -2y-9}\thinspace$ to find $x$ ${x = -2}{(-5)}{ - 9}$ $x = 10 - 9$ ${x = 1}$ You can also plug ${y = -5}$ into $\thinspace {-2x+y = -7}\thinspace$ and get the same answer for $x$ : ${-2x + }{(-5)}{= -7}$ ${x = 1}$